This invention generally relates to antivibration apparatus and more particularly relates to a vibration dampener for dampening the vibration of a tubular member, such as an instrumentation tube of the type typically found in nuclear power reactor pressure vessels.
However, before discussing the current state of the art, it is instructive first to briefly describe the structure and operation of a typical nuclear power reactor, which contains tubular members, such as instrumentation tubes. In this regard, a nuclear power reactor is a device for producing heat by the controlled fission of fissionable material. The fissionable material is in the form of fuel pellets disposed in an elongated hollow rod which serves as cladding for the fuel pellets. A plurality of the elongated rods are bundled together by a plurality of spaced-apart grids having open cells therein for receiving each fuel rod therethrough. Moreover, a plurality of elongated movable control rods slidably extend through preselected ones of the grid cells, not containing fuel rods, for controlling the fission process. A plurality of these fuel rod assemblies are grouped to define a nuclear reactor core, which is sealingly enclosed within a reactor pressure vessel. Liquid moderator coolant (i.e., demineralized water) is caused to flow past the rods of each fuel assembly for assisting in the fission process and for removing the heat produced by the fission process. The heat carried away by the liquid moderator coolant is ultimately transferred to a turbine-generator for generating electricity in a manner well known in the art of electric power generation.
Disposed in the reactor pressure vessel are an upper core plate and an upper support plate that is spaced above the upper core plate, the upper support plate and the upper core plate being horizontally disposed in the reactor pressure vessel. Each fuel assembly is vertically spaced apart from and located below the upper core plate. Moreover, vertically extending through the upper core plate and into each fuel assembly is at least one elongated instrumentation tube that houses at least one detector to measure desired core physics quantities (e.g., neutron flux) in the fuel assembly.
However, during normal operation of the reactor, the liquid moderator coolant circulating in the reactor pressure vessel causes vibration of the internal components, including the instrumentation tubes, which are disposed in the pressure vessel. Moreover, off-normal operation caused by seismic events and postulated accidents (e.g., loss-of-coolant accident) also causes vibration of the internal components, including the instrumentation tubes. It is desirable to dampen the vibration of the instrumentation tubes during normal and off-normal conditions because excessive vibration may lead to inaccurate measurement of core physics values and premature wear of the instrumentation tube.
Therefore, a problem in the art is to provide means for dampening vibration (i.e., decreasing the amplitude of vibration) of the instrumentation tube when the instrumentation tube is subjected to the normal vibrations caused by routine operation of the reactor and when the instrumentation tube is subjected to off-normal vibrations caused by seismic events and postulated accidents.
Anti-vibration devices are known. One such device is disclosed in U.S. Pat. No. 4,990,304 entitled "Instrumentation Tube Features For Reduction Of Coolant Flow-Induced Vibration Of Flux Thimble Tube" issued Feb. 5, 1991 in the name of John A. Rylatt and assigned to the assignee of the present application. This patent discloses dimples formed in an instrumentation tube to constrain a flux thimble tube within the instrumentation tube, the flux thimble tube containing a neutron flux detector. This patent also discloses inwardly-projecting spring fingers formed in the instrumentation tube to contact the flux thimble tube. Although this patent discloses dimples and spring fingers to constrain a flux thimble tube within an instrumentation tube, this patent does not appear to disclose a vibration dampener for dampening the vibration of a tubular member, as described and claimed herein.
Therefore, what is needed is a vibration dampener for dampening the vibration of a tubular member, such as an instrumentation tube of the type typically found in nuclear reactor pressure vessels.